The present invention generally relates to integrated circuit (IC) designs, and more particularly to a sub-bandgap reference voltage generator design.
The increase demand for portable devices and the technology scaling are driving down the supply voltages of digital circuits. Voltage reference generator is one of essential building blocks of many integrated circuits (ICs). The bandgap reference generators which can operate from 1V supply are widely used in DRAM and flash memories. A bandgap voltage reference must be, at least inherently, well-defined and insensitive to temperature, power supply and load variations.
The principle of the bandgap circuits relies on two groups of diode-connected bipolar junction transistors (BJT) running at different emitter current densities. By canceling the negative temperature dependence of the PN junctions in one group of transistors with the positive temperature dependence from a PTAT (proportional-to-absolute-temperature) circuit which includes the other group of transistors, a fixed DC voltage output, Vref, which doesn't change with temperature is generated. This voltage is typically 1.26 volts, which is approximately the bandgap of silicon.
An early attempt for the solution is a conventional bandgap reference circuit that uses conventional bipolar technology to create a stable low reference voltage at around 1.2 volts as described above. However, as IC design is now predominated by low power and low voltage objectives, recent IC design typically requires sub-1 volt operation regions. While some conventional bandgap reference circuits can operate at slightly below 1 volt, most of the known conventional bandgap reference circuits are not suitable for a supply voltage lower than 0.9 V.
Accordingly, it is desirable to provide an improved low-voltage sub-bandgap voltage reference circuit that can operate at or below 0.9 volt supply voltage. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.